A liquid crystal display device is basically constituted by a backlight and a liquid crystal display element or liquid crystal display panel. As the backlight, an edge-light-type backlight is commonly used in terms of miniaturization of the liquid crystal display device. In the edge-light-type backlight, at least one edge surface of a rectangular light guide is used as a light incident surface. Along the light incident edge surface, a linear or rod-like primary light source such as a straight tube fluorescent lamp or a point-like primary light source such as a light-emitting diode (LED) is disposed. Light emitted from the primary light source is made to enter the light incident edge surface of the light guide, introduced inside the light guide, and then emitted from a light emitting surface which is one of two main surfaces of the light guide. The light emitted from the light emitting surface of the light guide is diffused by a light diffusing element such as a light diffusing film disposed on the light emitting surface and a light deflecting element such as a prism sheet to be deflected to a required direction. Light is also emitted from a rear surface which is the other main surface of the two main surfaces of the light guide. In order to return this light to the light guide, a light reflecting element such as a light reflecting sheet is disposed opposite to the rear surface.
A light emitting mechanism or light emitting structure serving as an optical function structure for emitting, as needed, the light guided inside the light guide is formed in the light emitting surface or rear surface of the light guide. For example, as the light emitting mechanism, a fine concavo-convex structure like a moderately roughened surface or a lens array forming surface obtained by arranging a large number of elongated lenses is used.
As a method for forming such a fine concavo-convex structure, there is known a method that press-molds a translucent material such as an acrylic resin by using a molding machine including a molding member having a shape transfer surface formed by blasting or cutting (see PTL 1 and PTL 2).
Further, there is also a method that directly processes the translucent material to thereby form the light emitting mechanism. For example, PTL 3 discloses a light guide having a plurality of grooves as the fine concavo-convex structure which is obtained by irradiating a light guide surface with laser light in a scanning manner.
Further, there is also known a method that uses a light scattering agent or bubble as the light emitting mechanism. For example, PTL 4 discloses a light guide made of a foamed material foamed by application of radiation energy and heat energy.